Establishment of positive pressure in a room or other such enclosed space may prevent or decrease the entry of foreign substances into the space. Ordinary usage of the space, however, may cause a loss of the positive pressure that may allow the entry of foreign substances. For example, opening of a door or a window of a room may cause a loss of the positive pressure as air rushes out of the room to the lower pressure air outside of the room. Maintenance of the positive pressure during ordinary usage is a challenge.
In clean rooms used in highly sensitive manufacturing processes, such as semiconductor and pharmaceutical manufacturing, positive pressure is one of several protective features used to prevent contamination. To enable entry and exit of a room by personnel without losing the positive pressure, an airlock is typically provided at each passageway into and out of the room. This first airlock is coupled to a transition room that has its own, second airlock to the exterior of the system. One enters the transition room through the second airlock when the transition room is at the same pressure as the exterior air. The second airlock is closed and the pressure in the transition room is raised to match the pressure in the clean room. The first airlock is then opened and the clean room may be entered without a drop in the positive pressure in the room. In this way, the positive pressure is maintained. Other protective features to prevent contamination include the use of special clothing, slippers, masks, and cleaning procedures. On leaving the clean room, the user enters the same or another transition room at the same positive pressure as the safe room and the safe room airlock is closed. Then the user leaves the transition room through the second airlock. While effective, the use of airlocks and transition rooms is a complicated and expensive solution to the problem, which also requires a lot of space.
Hospitals also provide positive pressures in operating rooms to keep out contamination. Typically, airlocks are not used in operating rooms due to the cost and time delays involved. Some pressure drops are therefore tolerated when doors are opened for short periods of time. However, if a door is opened for a period of time that may result in a deleterious loss of pressure, such as 15-30 seconds, for example, an alarm may sound to alert users to check the door. Hospitals may also provide positive pressures in rooms containing patients with compromised immune systems to decrease the risk of infection.
Protection of individuals in their home against a chemical, biological or radiological incident, such as a terrorist attack or an accident, is of increasing concern. It has been recommended after a chemical, biological, or radiological terrorist attack, that doors and windows in a selected room in a house or apartment be sealed with plastic and masking tape to keep out dangerous substances. The degree of protection depends in part of the effectiveness of the sealing. While better sealing better prevents the entry of dangerous substances into the room, it may also prevent the entry of oxygen. Since the oxygen in a room may eventually be depleted, such a sealed room may only be occupied for a relatively short period of time.